It is known that a flat-plate transmission line mainly includes an insulating plate interposed between two metal sheets brought to different electric potentials. It is known to set up an electric discharge in a line of this type by means of a device which includes two opposed electrodes situated respectively on either side of the line and connected respectively to the two metal sheets of the flat-plate transmission line. These electrodes are generally aligned along an axis perpendicular to the plane of the flat-plate transmission line, the axis passing through a transversal opening in the transmission line. The device is provided with a system which is capable of triggering an electric discharge between the two electrodes. The discharge causes a current wave to be formed which propagates in the transmission line. The current wave excites the active material of a gas laser said gas laser; being disposed, for example, in a slot in one of the metal sheets of the transmission line.
After a few discharges, the operation of the device described above becomes unsatisfactory, since short-circuits appear between the metal sheets across the opening. These short-circuits are built up from metal deposits released by the electric discharges. To try to mitigate this disadvantage, circular surfaces have been disposed around the opening in the insulating plate. These surfaces are not covered by the metal sheets. The proper operation life of the device is thereby lengthened, but after some time, the metal deposits which occur also on these annular surfaces manage to form a conductive film which short-circuits the two metal sheets.
Preferred embodiments of the present invention remedy this disadvantage by producing a spark gap for a flat-plate transmission line which spark gap is capable of operating without incident during numerous successive discharges.